1. Field of the Invention
The present invention relates to a structure for holding an optical article, such as a lens and the like.
2. Description of the Related Art
In a conventional optical equipment, a holding frame or barrel is often used to hold an optical article such as a lens or a mirror. Such optical equipment usually requires a precise alignment of the optical axis of the optical article with respect to the center axis of the barrel. This is often very important, especially when the optical article is a lens. For the alignment, the barrel may have an inner peripheral surface of a shape that corresponds to that of an outer peripheral surface of the optical article. For example, when the article has an outer peripheral surface of a circular shape, the inner surface of the barrel may have an inner surface of a circular shape with a nearly equal diameter. However, the diameter of the former should be smaller than that of the latter if they are not interference-fit to each other. Therefore, in many cases, the barrel and the optical article are so sized as to provide either a small gap or a large gap therebetween.
In the former, with a small gap, it is easy to align the center of the optical article with the center of the barrel. However, the inner peripheral wall of the barrel and the outer peripheral surface of the optical article must be accurately finished or processed. Such a process results in an increased production cost. A further disadvantage of this arrangement is that edge chips, scratches or other undesirable flaws are likely to occur as a result a of contact of the optical article with the barrel, due to such a small gap.
In the latter, with a large gap, when a part of the outer peripheral surface of the optical article is in contact with the inner peripheral wall of the barrel, the center of the optical article is offset from the center of the barrel, which adversely affects the performance of an optical equipment. Thus, it is difficult to align the center of the optical article with the center of the barrel while holding the optical article, without using a retainer or screw to hold the optical article. However, such a retainer or screw is likely to loosen over a long period of time. This causes the optical article to be inconveniently offset from the barrel.